A digitally-controlled DC-DC converter has been widely used for the purpose of low power consumption, semiconductor integration, etc. In the digitally-controlled DC-DC converter, a pulse-width modulated signal having a duty ratio depending on the voltage difference between an output voltage and a reference voltage is generated by a DPWM circuit, a square wave voltage is generated by switching an input voltage based on this pulse-width modulated signal, and the output voltage is generated by smoothing the generated square wave voltage by a lowpass filter.
It is not easy to broaden the signal band of the digitally-controlled DC-DC converter. This is because the signal band must be limited to a low-frequency range which is less influenced by the delay occurring in ADC, DPWM circuit, etc. arranged in the digitally-controlled DC-DC converter.
Since the DPWM circuit generates a pulse-width modulated signal based on a result obtained by comparing a digital ramp wave signal with a duty signal, a delay time is generated between the input and output of the DPWM circuit, depending on the sampling frequency of the digital ramp wave signal and the duty ratio of the duty signal. When a load variation occurs while a delay is caused in the DPWM circuit, the output voltage cannot be controlled quickly and the output voltage greatly varies.
As a technique to prevent such a defect, it is suggested to switch to TOC (Time-Optimal Control) control when a load variation occurs, in order to recover the output voltage quickly. However, it is required to correctly grasp the element values of inductor, capacitor, etc. in the DC-DC converter to realize highly-accurate control. Since the element values change depending on environmental conditions such as temperature, it is difficult to perform highly-accurate control.